Historically, the badger was fairly common species in Naliboki Forest that is in the north-western part of Belarus. Besides the respective information that was obtained from the locals (e.g. Baliaslaw Sadowski, Lianard Jurevich, Edzik Khmara), who lived and was familiar with the forest in the 1930s-1960s, also presence of numerous former badger setts suggests about the commonness of badgers. Approximatelly, the density of main setts, where badger families lived before, was not lower than 15 per 100 km2 in the most ecologically rich southern part of Naliboki Forest and about 4 per 100 km2 in the central and central-northern parts of the terrain, where habitat carrying capacity for badgers is markedly lower. It means that the former density in more or less undisturbed badger population in Naliboki Forest ranged approximately between 20 and 120 individuals per 100 km2 in relation to the habitat carrying capacity of the terrain.
Excessive rate of illegal hunting that happened in the 1970s was evaluated as the main cause of badger decline in the whole Belarus (Daraphieyew et al., 1981), but seemingly there were other significant causes for the decline in badgers.
In summer 2007 in Naliboki Forest we censused seven active setts on the area of 690 km2, i.e. 1 active sett per 100 km2 and 2.6 inds per km2. In seven active setts found we revealed the following inhabitants: (1) 3 adults, 1 subadult, 2 cubs; (2) 1 adult; (3) 1 adult; (4) 1 adult; (5) 3 adults; (6) 2 adults, 2 cubs; (7) 2 adults. Only two out of seven active setts held litters (28.6 %). Approximate portion of juveniles was 22.2 %.
In summer 2008 in Naliboki Forest we censused again 7 active setts, but their locations were slightly different from that in summer 2007. So, we found about 1 active sett per 100 km2 and 1.9 inds per 100 km2. In seven active setts found we revealed the following inhabitants: (1) 2 adults; (2) 2 adults; (3) 1 adult; (4) 1 adult; (5) 1 adult; (6) 2 adults, 2 cubs; (7) 2 adults. Only one out of seven active setts held litters (14.3 %). Approximate portion of juveniles was 15.3 %.
In summer 2009 there we censused 5 active setts only, i.e. about 0.7 active sett per 100 km2 and 0.7 inds per 100 km2. In all five active setts we found solitary adult individuals only. No litter in the setts was revealed.
The estimated values of badger population density in Naliboki Forest were evidently very low and suggest strong decline in badgers there. Indeed, in the 2000s in Naliboki Forest on average we found only one active sett per 100 km2 and 1.9 inds per 100 km2 of fairly favourable habitats. For comparison it may be mentioned that on the same latitude in Scotland population density in badgers varied 1 – 8 (mean 2.2) inds/ km2. There, average family group consists of 5.4 (2-11) adult badgers (Kruuk & Parish, 1982). In contrast, in the 2000s in Naliboki Forest solitary badgers prevailed in the inhabitant composition of badger sett. 52.6% of active badger setts were occupied by lone badgers. Moreover, for instance, in Scotland Kruuk (1989) recorded that from 16 family group observations only 3 family groups had no litters, i.e. 81.3 % of active badger setts held a litter. In the 2000s in Naliboki Forest the occurrence of litters in active badger setts was greatly lower – about 16 %.
The last decades poaching of badgers in Naliboki Forest happens rarely, and that may suggest some kind of natural causes that lead to the strong decline in badgers there in the 2000s and earlier. Basing on the data obtained in Naliboki Forest and suitable information gained in other areas in Belarus (first of all, in Paazierre Forest) suggesting other factors of non-human origin, we produced several hypotheses for the decline causes and gradually proved them (Rotenko and Sidorovich, 2017). Here we only formulate the findings on the causes of the badger population decline, what is fairly sophisticated.
To clarify in advance the following complicated explanations, initially we would like to state that the current decline in badgers mainly happened because of a multi-way impact of the naturalized raccoon dog, while many other factors either enhanced the raccoon dogs’ impact or exacerbated directly the declining process in badgers. So, let us start with how the naturalized raccoon dog population destroys the badger population.
At first, during the harsh winter conditions, that were common in the whole Belarus and also in Naliboki Forest at least till the end of 2000s, badgers slept strongly, but raccoon dogs that overwintered in badger setts too, and they tended to be active from time to time especially during thaws. While hibernating together, raccoon dogs tried to separate from sleeping badgers in their setts by blocking underground tunnels with ground. In this case after being blocked by active raccoon dogs with ground badgers may die from suffocation inside the sleeping chambers. Approximately, about 10% of badgers died like that each year in the 2000s and earlier.
The second kind of negative influences of raccoon dogs was connected with the following: harshness of winter (first of all, long duration of winters); relatively low biomass of earthworms (one of the main nutritious food of badgers in many regions) in dry land habitats; and presence of large predators such as wolves and lynxes. While foraging, badgers tend to avoid the high predation risk coming from these large predators. Therefore, in the majority of cases badgers walked straight between their burrows (main sett and outliers) that are situated within dry land habitats mostly (Sidorovich et al., 2011; Rotenko and Sidorovich, 2017). With such a walking pattern badgers had not enough possibility to feed on earthworms in black alder swamps that are characterized by relatively high biomass of this nutritious food. Therefore, in such situation the only feeding strategy for badger was to be a scavenger and a generalist predator on small prey. Having such a feeding, badgers plausibly were not able to accumulate enough fat for long sleeping during the whole long winter that was more or less common till the mid of 2010s. Badgers have spent fat till the beginning of March and needed to forage in still snowy forest quite often a month long. In such conditions carrion that originated mostly from died wild ungulates was the only relevant food. However, numerous raccoon dogs that woke up, at least, a month earlier have already consumed all carrion in particular in the surrounding of badger setts. With such a competition for carrion badgers appeared almost without relevant food, being much outcompeted by raccoon dogs. In such a situation badgers starved and scavenged for poor-quality food. It is not rare that a part of badgers died from starvation, especially if winter lasted too much.
The third impact of raccoon dogs was a possible influence of diseases with implication for dense population of the alien species, i.e. the raccoon dog. Too frequent presence of raccoon dogs in badger setts and dense raccoon dog population creates greatly more favourable conditions for diseases circulation. In this case badgers that spend in setts the majority of time would be affected much harder by the diseases than raccoon dogs.
In Belarus in the 2000s and earlier being impacted so much by raccoon dogs and other unfavorable factors (see below), the majority of badger setts were occupied by lonely living badgers. Definitely this situation makes difficult for adult females to get pregnant during mating season. Even if lonely living adult female badger got pregnant, it may be hard to save litter, while living alone. Badger is a social species and one of the sociality features in badgers is alloparental behaviour (Woodroffe, 1993). Living alone or even in too small family groups, cubs appeared to stay alone for the periods of adult feeding. During this time cubs were not rarely attacked by other burrowing carnivores, i.e. red fox or raccoon dog that may breed in the same sett or an outlier nearby. That was the fourth kind of impact of raccoon dogs on badgers.
When the majority of badgers lived alone, in order to find a mate during the mating season they (especially males) needed to go far away from their more or less safe routes between the main sett and outliers. There is no doubt that, walking far away, badgers were killed by wolves and lynxes. Therefore the badger population density decreased again and fewer and fewer adult males remained in the population (usually 1-2 adult males per each 10 adult females). This situation impaired breeding rate. Again just the raccoon dog multi-impact initiated this breeding deterioration in badgers.
Besides the mentioned direct and indirect impacts of raccoon dogs on the badger population badgers were still killed by poachers, their setts were destroyed by heavy modern forestry techniques and the sleeping badges suffocated gradually therein. At the same time, in the 2000s and earlier this human impact was not the main one in comparison with the negative influence of raccoon dogs.
Since the end of 2000s in Naliboki Forest and its rural surroundings a decline in the raccoon dog population had happened. Actually there was registered the partial restoration of the local population of raccoon dogs in Naliboki Forest in 2012-2013, but then the number of raccoon dogs decreased considerably (6-10 fold) again. In effect the number of badgers and their occupation of setts increased gradually. In the summer of 2012 we censused about 9.6 badgers (3.7 active badger setts) per 100 km2 compared to 0.7 in 2009. This summer of 2012 14 out of the 30 active main badger setts registered (46.7%) contained a litter. In 2011 the same area the badger population density comprised about 5.5 badgers (2.3 active badger setts) per 100 km2; and 7 out of 17 active main badger setts registered (41.2%) contained a litter. In the summer of 2012 locally the species population density was markedly higher than the average one. On the area about 80 km2 at the Vialikaja Chapun’ village there were 4 active badger setts that were occupied by 19 badgers. There the badger density constituted 23.8 individuals per 100 km2. At the same time in the central part of Naliboki Forest, which is characterized by relatively low habitat carrying capacity for the species, the badger density was very low still – about 2.6 individuals per 100 km2.
After 2012 we stopped the terrain-wide monitoring of the local population of badgers in Naliboki Forest, nevertheless, since 2016 our 10 to 15 camera-traps traced the situation in the model badger setts almost year-round. Despite of the limited data on badgers after 2012 several changes in badgers in Naliboki Forest were evident and it is worthwhile to mention them.
Nowadays in Naliboki Forest badgers got mainly out of the former impacts of the alien raccoon dogs. Why that has happened? First, raccoon dogs got relatively rare in Naliboki Forest especially since 2015 due to the excessive predation on them by lynxes and wolves. In particular, numerous lynxes supressed the raccoon dog population by killing almost all cubs. So, there was no reproduction in raccoon dogs in Naliboki Forest anymore during the last years. Second, winters in Naliboki Forest got markedly milder and almost double shorter, perhaps, due to the climate change. During the relatively mild winter in Naliboki Forest badgers were registered to be active from time to time. They are able to send raccoon dogs away from the overwintering burrows and, in turn, the risk to get blocked by raccoon dogs in their sleeping chambers became actually very low. In effect, since 2015 in Naliboki Forest the badger got a common species with an approximate average density about 30 badgers per 100 km2. Again, there are more badgers in the south-western half of Naliboki Forest (approximately 30 to 50 inds per 100 km2) and fewer of them in the north-eastern half of the terrain (10 to 30 inds per 100 km2).
So, badgers in Naliboki Forest got much benefit from the presence of many wolves and lynxes, because these predators keep the low density of the local population of raccoon dogs. At the same time, these predators, particularly lynxes kill badgers as well. However, the pooled effect of that is positive for the badger population and the species got thriving in Naliboki Forest, at least, in 2015-2019.
Tracing the situation at the model badger setts by camera-traps suggests that lynxes visit setts almost year-round, and during the seasonal periods, when badgers are active a lot, lynxes tend to watch for them from an ambush or just by laying or sitting on the ground in the close proximity to the burrow entrances. Some impatient lynxes even try to enter the badger sett to scare badgers from their burrow. The frequency of lynx visits to a given sett evidently correlates with presence of badger cubs and the total number of badger in the sett, i.e. the availability of badgers as possible prey. As to wolves, they mostly visit badger sett in the denning period. If there are many badgers in a given sett wolf breeders usually do not try to kill them in order to occupy their sett for denning, because it is too much work in this too busy time. But lonely living badger may be deliberately killed by wolf breeders to occupy the sett for denning. Sometimes some badgers abandon their sett in May, when wolves start denning there. Breeding female lynx is characterized by similar pattern of denning behavioural features in a badger sett. In a large badger setts that consists of several not connected parts badgers seemingly peacefully coexist with breeding female lynx.